This invention relates to packaging apparatus, and more specifically to apparatus and procedures for heat sealing packaging materials, such as liners and bags having tubular mouths which must be closed and sealed. While the invention may be utilized to seal the mouths of diverse types of liners and bags, it will find particular utility in the sealing of lined cartons which, upon erection, are continuously advanced in a path of travel during which the mouths of the extended liners are sealed and infolded, followed by the infolding and sealing of the carton end closure flaps.
Numerous expedients have been heretofore employed to seal the mouths of the liners, depending upon the nature of the liner materials and their heat sealing characteristics. If the nature of the lining material is such that it may be directly contacted by the sealing elements, these expedients have included the use of heated metallic belts which travel with the lining material until the desired seal is effected, and also the use of traveling sets of jaws which engage the liner and move with it until sealing is effected, whereupon the jaws open and are returned for engagement with a succeeding liner. Other heat sealers have utilized radient heat or hot air to at least partially heat the liners in the areas to be sealed, followed by pressure rollers which compress the heated material to complete the seal.
A major disadvantage common to the foregoing types of heat sealing apparatus is the amount of space required to perform the heat sealing operation when the liners are being continuously advanced in a path of travel as an incident of the various filling, closing and sealing operations which must be performed. This is particularly true if the cartons and liners are running at a relatively high rate of speed. Effective sealing is a function of time, it being necessary to heat the liner material to sealing temperature and compress the material together to obtain the desired seal; and as the speed of travel increases, so does the amount of space required to maintain heating and sealing contact for the amount of time required to effect the desired seal. Since space is often at a premium, the problem becomes acute.
The present invention overcomes the foregoing difficulties by utilizing a sealing technique wherein the advancing liners are repeatedly contacted by an opposing pair of heating elements which move in orbital paths relative to each other and to the advancing liners. With such arrangement, the total time in which the sealing elements are in contact with each liner is sufficient to form the seal, yet due to their orbital movement during which the sealing elements repeatedly close against the liner, advance a short distance with it, open, and then retract for reclosing and reengagement with the same liner, the amount of spece required for the sealing operation is minimized.